Launch and Space vehicle systems utilize propellants maintained at cryogenic temperatures. Cryogenic temperatures include as low as −452 degrees Fahrenheit. As one example, liquid hydrogen and liquid oxygen are stored in separate propellant tanks and combined at the inlet of an engine prior to combustion. Not only must the propellants be stored and maintained at extremely cold temperatures, but to supply the engine(s) with liquid fuel and oxidizers or other propellant requires transferring the extremely cold propellant from the storage tanks to the engine(s). Also, as the temperature of extremely cold liquid propellants warms, the propellant undergoes a phase change and the liquid propellant transitions into a gas phase. Such warming occurs not only on the launch pad from ambient conditions, but in space from exposure to solar energy striking the launch vehicle. Such heating is absorbed by the propellants as the latent heat of vaporization with little to no change in sensible heat, meaning after fully converted to a gas, the propellant is still at the same cryogenic temperature. The management and conveyance of cryogenic gasses is equally important to launch and space vehicle systems as cryogenic fluids. As an example, the introduction of additional heat to a cryogenic gas in a closed system increases the pressure in the storage tanks, requiring venting of at least a portion of the gas to maintain desired pressures and temperatures within the tank. Similar to fuel supply lines, ducts for transporting and venting the gas must be able to withstand cryogenic temperatures.
Cryogenic temperatures are problematic for non-metallic materials because of the resulting poor properties, making most non-metallic materials weak and brittle. For this reason, metallic materials are used for transporting liquid and gas phase propellants at these cold temperatures. Metallic ducts have excellent properties at cryogenic temperatures and therefore exhibit excellent mechanical performance. However metallic solutions tend to be massive or require massive support systems in order to survive significant loading environments. The higher mass when combined with high vibration and other loads arising from launch and space vehicle environments can further result in high loads transferred to adjacent structures leading to damage or failure. Adjacent structures can include sensitive structural or payload elements, which can drive the need for additional supports or similar mitigations resulting in even more total system mass. To address the issues of escalating mass and resulting loads to interfacing hardware, metallic ducts of increasing complexity and cost have been designed to control mass on interface load escalation. For example, incorporating metallic bellows with various mechanical restraints has been utilized extensively reducing vibration response and load transfer. However bellows type solutions present new challenges such as squirm, bulging and fatigue induced by high vibration and load environments. Again, this leads to increasingly complex designs with increased expense and do not reduce weight in an appreciable or meaningful way and in some instances increase weight. Metallic ducts can present additional challenges such as galvanic corrosion and combustion when transporting pressurized oxygen. These and similar issues further result in more complex designs which increase expense and do not reduce weight in an appreciable or meaningful way.
WIPO Publication WO 2014/001429 (“the '429 publication”) describes flexible hose for carrying cryogenic fluid, specifically for transferring liquid natural gas from an off-shore tanker to an on-shore storage facility. More specifically, a hose is disclosed having an inner polymer wall surrounded by a corrugated metal duct with a coiled wire support wound through the corrugations, an outer fabric layer and a second wire support frame wound around the exterior of the fabric. The corrugated metal portion adds weight. The metals forming the duct and coil could cause galvanic corrosion. Moreover, the fabric layer, at a minimum, is a significant fire hazard. If the duct or hose contains pressurized cryogenic oxygen, an impact or puncture of duct or hose can result in combustion and explosion and the presence of the fabric layers facilitate and enhance this risk.
U.S. Pat. No. 4,445,543 (“the '543 patent”) also discloses a flexible hose for loading and offloading liquefied gases from tanker ships. The hose is made of multiple polypropylene film tubular bodies alternating with tubular bodies of polyethylene terephthalate cloth, an innermost and outermost wear resistant layer of polyethylene terephthalate cloth, and wires helically wound on the inside and outside of the bodies. Again, the cloth layers make this hose a significant combustion risk. Moreover, while the patent states the hose will remain flexible at temperatures down to −196 degrees Centigrade (approximately −320 degrees Fahrenheit), it does not teach or suggest the ability to handle cryogenic liquids below −320 degrees Fahrenheit.
Further still, hoses of the type described in the '429 publication and '543 patent present a further risk of perforation and/or occlusion. The annulus of space among and between the various layers existent in each of these hoses may fill with gas or liquid in the event of a failure or puncture of the inner fluid barrier layer. Gas or liquid would accumulate and could occlude the hose, preventing or reducing to inadequate levels any further propellant flow. Fluid accumulation in this interstitial gap also may rupture the hose, particularly as the ambient pressure decreases during vehicle ascent or approaches zero in the space environment. Fluid trapped in this gap may rupture an interior layer of the duct, or expand to occlude the flow path. The insulation space and fabric layers allow for the accumulation of gas and/or liquid and for the potential liquefaction of air if the space is not completely purged. As a result, these hoses would not have applicability at temperatures below approximately −300 degrees Fahrenheit because at temperatures below −300 degrees, the air would condense.
Another concern with launch vehicle/spacecraft applications is the sensitivity of the payload and surrounding composite vehicle structures. In addition to damage resulting from vibrations or load transfer, payloads and composite structures can be damaged by outgas emanating from polymers and epoxies. NASA has specified outgassing requirements for systems physically located in the same enclosure as composite vehicle structures or payloads.
Both the '429 application and '543 patent were clearly developed and intended for ground based industrial applications where mass is not important and survivability in high vibration and load environments are not a factor. This observation, in addition to the afore described specific failure scenarios, do not allow for these designs or any practical variants to be used for launch or space system applications.